626 PROF. H. G. SEELEY ON [Aug. I9OO, 



I am not able to count more than sixteen ribs in sequence on the 

 right side of the dorsal region, and am disposed to think that that 

 number includes the whole of the dorsal series. The earliest are 

 short. There appear to be indications of a few small sternal ribs, 

 between the interclavicle and the coracoids ; but the disturbed 

 preservation makes such identification of those ribs very uncertain. 

 Behind the region of the scapula the dorsal ribs attain their maximum 

 length, seen in about half-a-dozen long ribs which follow the first 

 few shorter ones. Then the ribs steadily decrease in length. 

 They are strong without being massive ; curved from above down- 

 ward and outward ; compressed from side to side ; and somewhat 

 flattened on the rounded dorsal surface. Their extremities terminate 

 abruptly in truncated surfaces. There is no indication of abdominal 

 ribs, such as characterize Hypevodapedon, Mesosaurus, Protorosaurus, 

 and the Plesiosaurs. 



The Sacrum. 



The transverse width of the sacrum is due to the elongation of 

 straight, horizontal, transverse processes or sacral ribs, which extend 

 outward at right angles to the axis of the vertebral column. 



Upon the upper half of the inner side of the left ilium above the 

 acetabulum there is an impressed area which covers the width of 

 the bone. It presumably indicates the articulation of the sacrum, 

 and may comprise four narrow, deep, vertical impressions of greatly 

 expanded ends of sacral ribs, as in Pareiasatirus, only longer. 



The Caudal Vertebrae. 



Behind the sacrum the vertebras rapidly become very short. 

 There are at least three vertebrae in close contact one with the other 

 indicated as resting upon the left ischium, and those vertebrae are 

 probably caudal though they are in close contact. Behind them, 

 separated by a slight interval, are indications of nine or ten vertebrae 

 which form the remainder of the tail. The bodies of the vertebrae 

 become successively shorter, and the interspaces between them are 

 well-marked. Their shortness is a distinctive character. The 

 neural arch is well developed, and in the first four vertebrae of the 

 series there appear to be short chevron-bones freely articulated. 

 The posterior surface of the centrum forms oblique facets for arti- 

 culation of the chevron-bones. 



The Shoulder-Girdle. (Fig. 3, p. 628.) 



The shoulder-girdle presumably includes nine bones, but I have 

 not recognized the clavicles. The remaining seven elements com- 

 prise five bones on the ventral surface. First a median T-shaped 

 interclavicle, which does not differ appreciably from the ' pickaxe '- 

 bone in Ichthyosaurus and Africau Anomodonts. Behind each of its 

 long lateral transverse bars is a pair of bones, thin and disc-shaped, 

 which are divided from those of the opposite side by the longitudinal 



